A MEMS (Micro Electro Mechanical Systems) mirror is known as a deflector for changing a reflection direction of an incident light (see, for example, JP-A-2006-201520). Specifically, this MEMS mirror comprises an oscillating mirror which oscillates rotationally, a mirror support body having an opening larger than the oscillating mirror, and a shank which connects the oscillating mirror and an edge part of the opening of the mirror support body.
Recently, it is considered that such MEMS mirror is applied as a scanning mirror for a light scanning device in an image forming apparatus such as a copying machine or a laser printer. In the case where the MEMS mirror is installed in such light scanning device, a light emitted from a light source passes through a lens or a diaphragm, and is projected onto the oscillating mirror of the MEMS mirror in which a reflection direction is properly changed by the rotational oscillation of the oscillating mirror.